Adhesion of spray droplets to foliage: The role of dynamic surface tension and advantages of organosilicone surfactants

Abstract

Measurements of the dynamic surface tension of seven surfactants (four organosilicones, two ‚conventional’︁ hydrocarbon‐based surfactants and an organosilicone + hydrocarbon‐based blend; 0.5 to 5.0 g litre−1) have been combined with data on the adhesion of their spray droplets to pea leaf. The latter were determined by a method enabling the surface age, and thus surface tension of the droplets at impact, to be calculated. Adhesion was directly related to the dynamic reduction in surface tension (2 to 50 mN m−1) prior to impact. The organosilicone surfactants and the blend reduced surface tension more rapidly and to lower values than did the organic surfactants. Adhesion was also inversely related to droplet size (110 to 880 μm diameter), droplet velocity (0.3 to 2.8 m s−1) and angle of incidence on the leaf (0 to 67.5 degrees). These physical factors were of less importance than surface tension in controlling adhesion. Relative adhesion varied among the surfactants both with their concentration and with surface tension. These findings are discussed with respect to their implications for the possible involvement of surface viscosity in the spray impaction process.

Efeitos de surfatantes sobre a tensão superficial e a área de molhamento de soluções de glyphosate sobre folhas de tiririca

“…O Silwet L-77 tem um bom coeficiente de eficácia, reduzindo rápido a tensão superficial, corroborando com os resultados obtidos por Stevens et al (1993).…”

“…A tensão superficial é um dos fatores chaves na performance dos surfatantes e sua redução é mais importante do que o tamanho da gota, velocidade da gota e ângulo de incidência na folha para a determinação da adesão nas folha (Stevens et al, 1993).…”

“…O mecanismo de ação dos surfatantes na superfície das folhas está correlacionado com o aumento da área de molhamento, dissolvemento ou na desruptura das ceras epicuticulares, solubilidade dos agroquímicos, prevenção ou atraso na formação de cristais do depósito, retenção de umidade pela sua ação umectante e aumento da absorção das soluções via infiltração estomatal (Stock & Holloway, 1993). A redução da tensão superficial a 28-32 dina/cm induzida por surfatantes leva a uma penetração estomatal em folhas de Pyrus communis L. (Greene & Bucovac, 1974).…”

Spray Retention of Crop Protection Agrochemicals on the Plant Surface

“…Organosilicone surfactants can reduce the surface tension of spray droplets more significantly than other surfactants, but their effect on spray droplet VMD is not consistent in the published literature. Stevens et al (32,33) reported that the VMD of spray droplets with organosilicone surfactants can be reduced to a significantly greater degree than conventional surfactants, but Holloway et al (25) actually observed the opposite effect in that VMD of droplets increased significantly when organosilicone surfactants were used. The different spray nozzles and spray pressure, as well as other ingredients in the spray solution, could be the cause of the observed discrepancy.…”

Pine oil increases spray retention by oats

“…Since the rate of diffusion to the droplet surface tends to be inversely related to molecular size [9], the diffusion coefficient of monoterpene alcohols in water is much higher than surfactant. This property allows a reduction in surface tension in 2-3 ms of relatively high VMD droplets that are flattened on impact, and a reduction in their bounce.…”